New Hornby Terrier DCC doubts

[pendeenpete]

I recently acquired a DCC fitted BR A1X from eBay in first class condition ,

Unfortunately the decoder blew after it ran for about 3 feet. I tried all the usual, resetting it etc, but eventually gave up as it was getting extremely warm. I run all my loco's on my Roco z21 without issue, including two TTS diesels.

I checked for shorts on the pins at the rear of the decoder socket without finding any, then made up a blanking plate from the dead decoder as Hornby don't appear to supply one. It then ran perfectly on DC for about an hour to run it in.

I have purchased a replacement Hornby 6 pin decoder, which is in the post. Now worried if there is a fault with the loco, this will also burn out. Just to be clear, I checked for continuity from the wheels and motor to the back of the decoder socket, and it runs without issue. Any thoughts on what else I could check before sacrificing another decoder?

[ColinB]

It is probably the decoder, Hornby decoders seem to have an issue with heat dissipation. The decoder wasn't encased in heat shrink by chance? I doubt there is anything wrong with the wiring as it would have blown up immediately. The only other thing to check is that the motor isn't shorting to the chassis/Wheels when it goes round a piece of curved track. That is what happened with an Oxford loco of mine. I have never measured the current on these but I use a Zimo one in my Terrier which has a slightly higher current rating 0.8 verses 0.5 amps.

[pendeenpete]

That's interesting, the decoder was bound up with insulating tape like an Egyptian mummy, I've ordered Kapton tape which is supposed to dissipate heat, Fingers crossed, as for a cheap decoder, they are very much not cheap! Tried to get another make, but due to the space available,every shop I asked said that the Hornby one was the only one guaranteed to fit.

[5Dublo2]

I have fitted Gaugemaster Ruby DCC93 Decoders into Hornby Terriers.

You do have to pop the socket out of the clips it sits in, then slightly uncoil the wiring to the back of the socket so that you can sit the socket and new decoder at an angle above the clip.

I will be replacing a Hornby decoder in a Terrier with a Gaugemaster one this weekend so will try and post images.

Note: my reason for replacing the Hornby decoder is not a failure, I want to be able to adjust the Speed settings (CV2, 5 & 6), along with Acceleration & Deceleration CV 3 & 4), and the Hornby's decoders don't let you do the speed ones

[pendeenpete]

Thanks for your reply, I did consider the Gaugemaster decoder, but they said it would need modification to the loco (unspecified), so I decided to risk another Hornby one.

I saw a you tube video where the author ( Worthington model railway) had blown 3 decoders consecutively. None of these were Hornby and the ones he tried fitting were not ideal size wise, but did nothing for my confidence.

Does the socket come out easily from the clips? I am thinking the only place I haven't checked is the bottom of the socket.

[ColinB]

It is a shame that there is a shortage of Zimo decoders at the moment. I found that the 6 pin one was very small and fitted mostly everything. It also has a output current limit of 0.8 amps which is good enough for most locos. On some occasions I have ordered the 6 pin wired one and rewired it to 8 pin as was the case with the Hornby class 87. I have never had that much success with Gaugemaster decoders but that could be me.

[5Dublo2]

A comparison shot showing the Hornby R7150 (harnessed) 6-Pin DCC decoder against the Gaugemaster DCC93 (direct plug). As the image shows the DCC93 is longer than the plug on the end of the harness which means it is too long to use without moving the socket in the loco. I do recommend trimming approx 1mm off the pins on the DCC93 before fitting. This is because the pins as supplied are longer than the holes in Hornby's socket (see the difference in length of the exposed pins in the image)

Luckily the socket in the loco is held in by a clip and also has spare length on the wires. The easiest way to unclip it is slide the socket forwards so that the black plastic block is no longer in the arms of the clip and then tilt the socket assembly upwards from one side.

Once clear of the clip if you turn the socket the other way up, which will unravel the wires slightly (do this carefully as you don't want to snap the wires off the PCB) This gives more play on the wires and then with the DCC93 plugged in you can place the DCC socket and decoder inclined above the clip (shown by the white arrow).

The body can then be refitted to the chassis.

As for extra insulation, situated like that the decoder assembly can't move very far and the only metal that could be touched is the red metal under the clip (and Hornby have helpfully already insulated that ) - as such I'd say the amount of tape added by Hornby around the decoder in the DCC fitted version is overkill and definitely won't help with heat dissipation

Note: You could generate a little more space by removing the clip (or the arms of the clip) - I chose not to do that so that I can easily return the loco to factory spec

[pendeenpete]

Wow, thanks for such an in depth answer, I've received the hornby 6 pin, and tried it without the body, thankfully it ran fine, now more confident,

[pendeenpete]

Oh dear, even more unseen problems with my Terrier, the collector plate that has plungers going to the base plate has a broken (or missing) spring on one side. As the spring is internal I can't see what could have broken it.

I have now had to get a new decoder,new motor and now this collector. All of them have been faulty, the motor would stall and need a spin of the worm to get going again.

Just a query, I can't remove the base plate completely, it seems to pivot on the rear brake rodding (after removing the screws!). Does it come off?

I'll get there in the end😳

[Brew Man]

From memory the brake rodding and the base plate do come off but it's a bit of a faff. I had to replace the pickups on one of mine a while ago. Unfortunately I can't check ATM as I'm out of the country.

[pendeenpete]

Just to say thanks to those who replied and to let you know the Terrier is now running with it's horrible Hornby decoder. I managed to not blow up all of the 6 pin decoders,and needed one of them for my Hattons P class (don't ask !).

If the Terrier maintains it's unusual behaviour of running, I may get a decent decoder for it in the future.

As the Hornby decoder does not have adjustable start voltage, I think it's set to low so the motor chatters a bit until it gets going, not too much, but it's there.

All in all, my worst eBay bargain🤔

[pendeenpete]

5Dublo2, thought I would let you know I followed your recommendation and fitted the Ruby decoder as described (Christmas present).

The improvement in the Terrier is quite amazing, the slow running is very smooth and the motor chatter has disappeared.

Thanks again

[5Dublo2]

@pendeenpete - glad my info helped